failed to start vm after add vsock device

[Michal Privoznik]

On 1/28/21 12:08 PM, longguang.yue wrote:
> 
> Michal, thanks.
> 
> i have another question  which is related to kata-container.
> 
> when there is only one  virtiofs-device , how does it do that   in guest there are 4 times of virtiofs-mounts that have same src and different targets.
> 
> # in guest
> [root at kvm kata-containers]# docker exec efda32ca6a93 mount | grep kataShared
> kataShared on / type virtiofs (rw,relatime)
> kataShared on /etc/resolv.conf type virtiofs (rw,relatime)
> kataShared on /etc/hostname type virtiofs (rw,relatime)
> kataShared on /etc/hosts type virtiofs (rw,relatime)
> 

I'm not sure how this is related to libvirt, but I'll try to answer 
anyway. I believe these mount points are set up by the initrd in the 
guest. And this confusion you are seeing is not related to virtiofs at 
all. It's non-intuitive way of how 'mount' shows bind mounts. One can 
bind mount a file. For instance:

   # touch /tmp/a /tmp/b
   # mount --bind /tmp/a /tmp/b
   # mount | grep /tmp/b
   tmpfs on /tmp/b type tmpfs 
(rw,nosuid,nodev,seclabel,nr_inodes=409600,inode64)

As you can see, mount doesn't show /tmp/a as the source of the mount 
point but the FS associated. And I believe this is what's happening. 
kataShared is mount as root, but then those three files from /etc are 
bind mounted and thus mount shows kataShared as their source. I agree 
it's misleading (and I remember running into this same problem when 
developing private namespaces for QEMU VMs - but that's another story).

Michal